Stock consistency transmitter

Abstract

An electro-optical meter for indicating consistency of a liquid slurry, employs a light source and a detector of backscattered radiation. The light is caused to scan the slurry while holding the light intensity and the peak-to-peak value of the detected signal constant. The distribution of backscattered light is measured and the minimum to maximum intensity of backscattered light is controlled.

I claim: 
     
       1. A method for electro-optically determining the consistency of a fibrous slurry, or other dispersed reflective suspension, the steps comprising: a. projecting a beam of light into the slurry;   b. detecting with a photo-detector, light reflected from particles suspended in the slurry while causing cyclical repetitive relative movement between the detector and the light beam so that the electrical output of the detector is substantially a sawtooth AC voltage;   c. controlling the intensity of the light beam to hold the peak-to-peak value of said AC voltage constant;   d. converting said voltage to a square wave form, squaring at 50% of peak-to-peak value, and measuring the ratio of the time of positive to the time of negative portions of the square wave to derive a signal proportional to consistency and substantially independent of brightness of, material being measured and light absorption by the liquid portion of the slurry.   
     
     
       2. A method as defined by claim 1 in which the position of said detector is fixed and said light beam is caused to scan the slurry in a cyclical repetitive straight line pattern with respect to said detector. 
     
     
       3. A method as defined by claim 1 in which the slurry is moving by a measuring window. 
     
     
       4. A method as defined by claim 2 in which the slurry is moving by a measuring window. 
     
     
       5. Apparatus for electro-optically determining the consistency of a slurry comprising: a. means for projecting a beam of light from a source into the slurry;   b. a photo-detector adjacent said means for detecting light reflected from particles suspended in the slurry;   c. scanning means for causing a cyclical repetitive movement between said detector and said light beam so that the electrical output of said photo-detector is a substantially sawtooth AC voltage;   d. control means interconnecting the output of said detector and said light source to hold the peak-to-peak value of said voltage constant;   e. means connected to convert said voltage to a square wave form, squaring at 50% of peak-to-peak value and;   f. means to measure the ratio of the positive to the negative times of said square wave to provide a signal proportional to said slurry consistency but independent of slurry brightness and light absorption by the liquid portion of the slurry.   
     
     
       6. Apparatus as defined by claim 5 in which said slurry is flowing past a transparent window and said first means and said photo-detector are positioned adjacent said window. 
     
     
       7. Apparatus as defined by claim 5 in which the position of said detector is fixed and said scanning means moves said light beam with respect to said detector. 
     
     
       8. Apparatus as defined by claim 6 in which the position of said detector is fixed and said scanning means moves said light beam with respect to said detector.